Vertical cavity surface emitting lasers (VCSEL) include a first distributed Bragg reflector (DBR), also referred to as a mirror stack, formed on top of a substrate by semiconductor manufacturing techniques, an active region formed on top of the first mirror stack, and a second mirror stack formed on top of the active region. The VCSEL is driven by current forced through the active region, typically achieved by providing a first contact on the reverse side of the substrate and a second contact on top of the second mirror stack.
The use of mirror stacks in VCSELs is well established in the art. Typically, mirror stacks are formed of multiple pairs of layers often referred to as mirror pairs. The pairs of layers are formed of a material system generally consisting of two materials having different indices of refraction and being easily lattice matched to the other portions of the VCSEL. For example, a GaAs based VCSEL typically uses an Al.sub.x1 Ga.sub.1-x1 As.backslash.Al.sub.x2 Ga.sub.1-x2 As material system wherein the different refractive index of each layer of a pair is achieved by altering the aluminum content x1 and x2 in the layers, more particularly the aluminum content x1 ranges from 0% to 50% and the aluminum content of x2 ranges from 50% to 100%. In conventional devices, the number of mirror pairs per stack may range from 20-40 pairs to achieve a high percentage of reflectivity, depending on the difference between the refractive indices of the layers. The large number of pairs increases the percentage of reflected light.
In conventional VCSELs, conventional material systems perform adequately. However, new products are being developed, such as CD write devices and those utilizing infrared data links, that require VCSELs to operate in a high power single mode. In general, VCSELs typically operate in a multimode due to carrier spatial hole burning and ring p-side metal contact induced current crowding effect. Such a carrier distribution will support multimode operation due to higher modal gain for high order modes. In that single mode operation is sought, some way must be adopted to fill the hole in the carrier distribution so that the single mode beam will see a higher modal gain.
Thus, there is a need for developing a reliable, stable and cost effective vertical cavity surface emitting laser (VCSEL) for use in high power single mode operations, that includes improved carrier distribution so as to allow for single mode beam operation with higher modal gain.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art. Accordingly, it is an object of the present invention to provide a new and improved VCSEL for use in high power single mode operations.
Another object of the invention is to provide a reliable high power single mode VCSEL.
And another object of the immediate invention is to provide for efficient carrier distribution in a high power single mode VCSEL.
Still another object of the invention is to provide for a higher model gain in a high power single mode VCSEL.
Yet another object of the invention is to provide for a highly manufacturable high power single mode VCSEL.